Image scaling property should not be used with checkboxes.

I'm getting some warnings with my project (that was originally Leopard, but migrating to SL). They're all for my XIB files, and say that "The image scaling property should not be used with checkboxes." Okay, that's fine, but I don't know what to do with it.

I have three checkboxes, and as far as I can tell, I didn't resize them. They're the same size as system checkboxes. Do I need to change how they're labeled?